Electrophotographic printers having an LED array as an exposure light source have been employed as a terminal for personal computers and work stations. In the conventional electrophotographic printers, the LED array is comprised of LED array chips each of which is made up of a plurality of LED elements formed on a single chip and arranged in a column. The LED array chips are disposed side by side in a line to provide a required dimension corresponding to the width of recording paper.
Because the brightness may vary from one LED array chip to another, it is necessary, in forming a line of LED array chips, to select chips having identical brightness. As a result, yield of chips is low. Moreover, the assembly takes much labor, resulting in a higher cost.
To improve this situation, electrophotograhic serial printer employing a single LED array chip have been proposed (Japanese Patent Kokoku Publication No. 23033/1985, and Japanese Patent Kokoku Publication No. 23034/1985). The electrophotograhic serial printers have a carriage moving back and fourth in a direction perpendicular to the direction of recording paper feeding, and devices for the respective processes of the electrophotography (charging, exposure, development, transfer, fixing and cleaning) are mounted on the carriage. Magnetic toner images formed on a photosensitive member are transferred to the recording paper, utilizing the magnetic forces, and fixed by applying heat from a heat source to the toner on the recording paper.
Systems using electrostatic forces to transfer toner images to the recording paper have also been proposed (Japanese Patent Kokai Publication No. 152463/1986). Transfer of the toner to the recording paper is made for a certain number of printing lines and the recording paper with the toner image unfixed is transported to a fixing means where the toner image is fixed.
A problem associated with the above prior-art electrophotographic printer is that a carriage moving in the line direction is mounted with all devices, i.e., charging, exposure, developing, fixing, etc., required by the processes of electrophotographic recording, rendering the mechanism complex.
For example the photosensitive member, developing device, charging device and so on require driving and transmission means for their rotation, and electrical signals are required to supply data for required charging and developing processes. A means for supplying electric power and electrical signals to a laterally moving carriage is complex, and there is a danger of disconnection (e.g., wire breaking) faults due to contact friction. Further, the many devices mounted on the carriage increase its mass thereby requiring a drive source and medium for transmission of power to be larger and stronger.